Purification of mustard gas



12, 1954 c. c. PRICE ETAL PURIFICATION OF MUSTARD GAS Filed March 14, 1945 kbbQQQK kwk SMIWQQ grwmvboms CHARLES C. PRICE ORVILLE H. BULLITT, JR. HERBERT E. HUDSON, JR. ARTHUR M. BUSWELL $34 54M Patented Oct. 12, 1954 2,691,626 oFsieE PURIFICATION" OF MUSTARD GAS I Charles g -ih'ice, Urbana, Ill., Orvi lle H. Bullit t,

United states 'of 1 6 Americans represented bythe secretanynfiwar. Application -Mar ch 14, 1945SeriztIN5E 582320 s Claimsfl (01.262-60T 12 The invention descrilied'herein 'may be manu' factured and used by or fdr tne Governinent-ior gevernmental pui poses without itl-ie 5 ayment to us of any'royalty tnereonr t This invention '=relate's -t6- a"'-proeess of purify- 2; to'the preblem ot-purifying and stabilizing Levin stein =rnustard= since its earliest; preparation and use but none of the methods-tried-gave any par ticulap-I promise= for-- large scale application.

5 object of this--inventionto' provide an ing Levinstein mustard. ln 'aceordanc with this efiicient method of treatmentfor purifyingnand inventiiam substantiallW'pure' mustard nlay-' be stabilizing:rLevinstein mustard 7 pz epaved from nevinstm mustard-ayesimple Another object of this invention isto-provide and inexpensiveltreatmentfi a -practioal' method; of treatment --forpurifying The 'agent known as mu'stard or' mustafidgas 10 and stabilizing'Levinsteinmustard-for applicationis the nfos't important chemical watfare'vesieant on adarge scale.- knownsto uatee- Cliemieal'li fpure' mustard is' re- In accordance-"with one-embodimentof this"- gande'd as 'being dichloroethyl sulfide} invention, iLevinstein mustard isfirst washed Although there have' been several processes with a quantitywofwater-andthe washed prod fo'r manufacturing miistardg themost important uct-is-thereafter subjected-to distillation to -proin this' ceuntry is tlie :Lev-inst-in process?" The duce' the desired product. A- relativelyt'large product oi "the Levinstein pi'ocess is commonlyi quantity of Water may beemployed intheinitial known to thos'e skille'd the ai t as Levinstein washing-step whichmay-be carried-outanumben mustardd 6 oitimesdf desiredi- After the Levinstein mus- In the Levinstein process, mustard is formed tard has been thoroughly washed,-the washby:direetrreactionzofietnyieneseas on sulfur-monowaterisseparated and-the'washedproduct is'subs" chlotidi While this reaotitin 'under proper- 0011 jeeted -to distillation,preferably ."under reduced ditidmproceed smoothly;'sulfui' is set"fired-farm pressures-t V Decomposition during distillation is* the temperaturdmust be eontfiolled'in order -to markedly lessthan-for unwashed-Levinstein,-and= keep the sulfur: in colloidal 'susp'ensioni There is the initial fractions of--the-distil-lation contaim considerable diiiloultyfiin sepamatiiig the mustard. water-white mustard-of a high order of purity: mom: the' lcolloidail isuliurp and aecor'dinglyfithe Thedistillationispreferably continued until thereacfliionfproduct hasbeen hitherto runto settling distillate beg-ins" to show evidence of the pres-- oristoragetanksthen'used: directly fonsnell filling ence o? color-formingwbodiesw withoutlfurtherstreatment. The im-provementin the distillation-after Levi-nstein mustar d' is a :relativly impure prodwater washing seems to b e due in 'part I to the-- uct;:its dichloroethylsulfide content-'being -in the removal -orinactivation by water of some im-- neighborhood Of.:70%. The impur-ities: of: Levinpurity :orimpurities which-lead todecomposition steintmust'ard are of-a complexnatureand have on heating,.--sinee distillation of-the unwashed not been completely determined. material Wasaccompanied flby-markedly greater- Although? the impure'iLevinstein mustard has decomposition during distillation. efiective-#vesieantfipropertiesr it hasthe serious- In thefollowing :are presented two specific exobjection of being-eunstab-le, .especially.on-'-pro'-=-" amples of the manner-in which this-irtiventioI-1 longedstorageinsteei eontainers andatelevatd has been carried out-:- temperaturem Theiexact-reasonfonthe degrada 40 Emmpwl 1 tion of Levinstein mustard has not been fully g 4 determined, however? the instability is apparent- A samplefof "twohundred "and"sevent"y'-one l ntdtieitoiicertain impurities since' thepu-r'e'prodgrams" of fLevihstein" mustard that had been uct'is not iunstableinnden the same conditions. thoroughlywashed four times with one hundred Ffom na pnaeticabstandpoint; it is-neoessary tovolumes of ita'p Water-was fractionallyvdistilledstore' lar'g'e strategic deservesonmustard in 'steel at reduced pressure, One hundred -andthirty-' drhms and-tomaintainlarge quantities intropithree grams of material distilled before -decpmcal -'climatee==wheredegradation oftli impure position oflthe residue became so great thata mnstatrd is hastened flWhen thimpuremustardvac'uum could no longer be obtained-A The dis"- undetgoes deterioration}pressures-develop'inthe tilling column was then replaced by a stillhad steeluirums and tlin it'-'-beoomes *necessary*to and 18g... more was distilled. 'Ifhus' a totalof destroy the fleteriorated'material; 151g. or 56 percent of the'starting inaterialdis A- great emount 'of researchhas ben devoted tilled? Freeman 2 3 z z g fi -3;; Color 0&6?

A sample of 1100 g. of Levinstein was stirred with water until the weight of unhydrolyzed material was 890 g. The washed material was distilled from a Claisen flask. The first two fractions, amounting to 451 g. and 119 g. respectively, boiled at 59 (1 mm.) and had 11. 1.5281 and 1.5284 (pure mustard; 11. 1.5276). These fractions were water-white and had only a very faint odor. The third fraction amounted to 163 g., was yellow in color, foul in odor, and boiled at 59 to 120 (1 to 4 mm).

On a large plant scale, the method has proved to be even still more efficient. A satisfactory method of application on a large scale will be described with reference to the accompanying flow diagram.

Referring to the flow diagram, crude Levinstein mustard from storage tank 1 is passed to wash vessel 2 wherein it is mixed with water from supply line 3, agitated and settled. The washed mustard is withdrawn from vessel 2 through line 4 to wet storage tank 5.

The washed mustard may be passed directly from line 4 or from the wet storage tank 5 to suitable distillation apparatus such as still 6, which is preferably of corrosion resistant construction, but it is often desirable to predry the washed mustard intermediately before distillation, particularly in large scale operations.

For the predrying the washed mustard may be heated in a suitable apparatus, such as a steam jacketed pipe or coil 1, and sprayed into a tank 8 maintained under vacuum applied through vent 9. The temperature to which the charge of Washed mustard is preheated depends on the vacuum, but it should be preferably below the boiling temperature of the mustard at the existing pressure and such that the vapor pressure of water is greater than the existing pressure. Suitable conditions for drying are about 60 C. and 5 mm. of mercury, although these may be varied, e. g., between 25 C. at about 10 mm. of mercury to 200 C. at atmosphere temperature.

During and following admission of the wet mustard to the dryer, air or similar inert drying gas may be run through the mustard to aid in removal of water and water vapor. Air may be used in any amount, but as the amount of air or drying gas is increased, the losses of mustard by vaporization are increased. The drying may be carried out by spraying the mustard into a packed tower with about equal effectiveness.

The mustard may be dried to a still lower water content by addition of a reactive drying agent, e. g., by adding small amounts of thionyl chloride. Thionyl chloride reacts with water to form sulfur dioxide and hydrogen chloride, which are gases readily removed from the mustard by heating and/or subjecting to vacuum. This reaction takes place over a wide temperature range but is preferably carried out between the melting point of crude mustard (5 C. to 9 C.) and the boiling point of thinoyl chloride (78 C.).

It is highly desirable to remove the last traces of water from the crude in order that this water will not distill with the first part of the mustard in the distillation step, thereby eliminating the 4 necessity for discarding or re-cycling an initial wet portion of the distillate.

The pre-dried mustard charge for the still 6 may be preheated in a suitable apparatus such as a steam liquid exchanger or preheater l2 in order to eliminate the necessity for cooling the still between batches and to decrease the amount of heat to be added in the still. The amount of preheat added may be varied, but the charge is conveniently, heated to approximately the same temperature as the boiling point of the material in the still pot at the existing pressure. Higher or lower temperature may be used but preferably a. maximum of about 250 C. is used.

The still 6 is provided with reflux condensers l3, having a vapor inlet connection I4 and a vacuum connection 15.; Reflux condensate is withdrawn from the condensers through line IE to receivers l1 and I8.

Heat is applied to the distillation vessel 5 in any convenient manner and high or low vacuum is applied to the system through line 15. The vacuum is preferably mm. of mercury or lower in order to reduce loss and contamination of the product through thionyl chloride decomposition products. Under 50 mm. mercury absolute pressure, the distillation may he carried out at a still bottom temperature of C., increasing to 175 C. as the distillation progresses, and a still vapor temperature of about 130-140 C. may then be maintained. Distillation is stopped when the flow of condensate slows.

Using a plant process as above outlined, approximately 90% of the dichloroethyl sulfide in the Levinstein mustard charge is recovered as purified mustard of about 95-97% purity.

The distilled mustard may be further improved is stability and purity by passing the distillate through a bed of solid caustic soda (sodium hydroxide) preferably in flake or lump form. The time of contact with the caustic will vary with the size and shape of the solid caustic, but it has been found satisfactory to pass the mustard distillate over commercial flake caustic at a rate of about 1 gallon per gallon of flake caustic at temperatures preferably below 50 C.

The further purification treatment is similarly effective if potassium hydroxide, calcium oxide, barium oxide or the like is used.

The following example demonstrates the purification of Levinstein mustard on a plant scale:

Example 3 For washing, to a 500 gallon glass-lined kettle equiped with an agitator was added 3,000 lbs. of crude Levinstein mustard (approximately 70% dichloroethyl sulfide), 300 cc. of anti-emulsion agent (Tret-o-lite L 17910) and gallons of water. This mixture was agitated vigorously for about five minutes. Agitation was stopped and the material was allowed to sepathe charging period, air was admitted beneath the surface of the liquid through a distributor at a rate of 5 cu. ft. of free air per minute; and the air flow was maintained for twenty minutes after the 300 gallon charge had been admitted. The water content of the charge was reduced to about 0.05% by weight.

For final drying, 60 lbs. of thionyl chloride were added to the vacuum dried charge to obtain thorough mixing. Sulfur dioxide and hydrogen chloride evolved were sent to a suitable absorption apparatus (not shown). The reaction was complete in about five minutes at the existing temperature of 60 C. The dried crude was drawn through a preheater of stainless steel, wherein it was heated to about 120-130 C. and finally discharged into a 500 gallon glass-lined still port fitted with an agitator, stainless steel condensers, receivers and jacketed for heating by means of steam, hot oil or Dowtherm liquid at about 200- 220 C. The absolute pressure was maintained at about 50 mm. of mercury. The vapor temperature was maintained at about l30-140 C. throughout the distillation. The flow of condensate started immediately and the distillation was continued until the flow of condensate slowed and the evolution of non-condensable decomposition product was observed in the vacuum line. The condensate product was found to be approximately 2,000 lbs. of purified mustard having about 95-98% purity.

It is to be understood that this invention is not to be limited by the detailed proportions and conditions set forth in the foregoing example.

The washing process apparently removes water soluble impurities, including salts, especially those of iron, which cause decomposition of mustard during distillation.

The amount of water used in the washing may be varied from about 1 the volume of crude mustard to more than an equal volume of water; about one-half volume of water is preferred.

The temperature of washing may be varied from about C. to 80 0., although at higher temperature hydrolysis of mustard by the water tends to cause larger loss and the hydrochloric acid formed by the hydrolysis may tend to prevent removal of iron salts from the mustard if the washing is permitted to proceed for exceedingly long periods (e. g., over approximately ten minutes at 80 C.). It is desirable that the hydrochloric content in the water layer should not be more than about for most efiective washing, because at higher acid concentrations the removal of iron salts becomes less complete. Accordingly, it is preferred that in the washing the amount of hydrolysis should not exceed about 20% based on the weight of the crude Levinstein mustard subjected to the washing, but in general, from about 5% to 20% of hydrolysis may be expected in the washing.

In a number of instances, it has been found difficult to separate the water and mustard layers satisfactorily due to emulsification. This difilculty is best overcome by addition of emulsionprevention or demulsifiers, such as Tret-o-lite compounds (products of the Tret-o-lite Co., St. Louis, Mo., between about 0.01 and 5% by weight. These agents are of a well known type which demulsify water in organic oil emulsions.

The purified Levinstein mustard obtained in accordance with the treatment of the present invention may have incorporated various stabilizing additives as desired such as anti-oxidants, corrosion inhibitors, and agents which reduce acidity or deleterious effects of impurities. A number of such additives mixed in economical and practical small proportions on the order of 1% give only slight increase in stability to crude Levinstein mustard but not sufficient to warrant their use as stabilizers in the crude mustard. However, they may be used more satisfactorily as additives in the purified mustard. Examples of such stabilizing additives are certain amines, such as alkyl amines.

The principal features of the invention reside in the steps of washing the crude with water and the distillation. Additional steps involved are useful in improving the process, but may be omitted without causing the process to be ineffective. A number of such additional steps are subject matter claimed in a co-pending application Serial No. 598,200, now abandoned, filed by W. L. Rippetoe, Jr. and A. G. Deem on June 7, 1945. Drying with a reactive agent such as thionyl chloride is subject matter of co-pending application Serial No. 596,719 filed May 30, 1945, for Chemical Process, by L. E. Simerl.

This invention is not to be lmited'to any of the examples which have been presented for explanation of the described process, since there are various modifications which come within the scope of the invention as defined in the following claims.

We claim:

1. A process of preparing purified mustard from Levinstein mustard which comprises washing Levinstein mustard with water, separating the washed mustard from the wash water, heating said mustard to a temperature below the boiling temperature of said mustard at the existing pressure, and thereafter distilling the washed mustard under reduced pressure to obtain a mustard distillate of a high degree of purity.

2. The method of preparing purified mustard from Levinstein mustard that includes in sequence the following steps: mixing said mustard with wash water; settling said mixture; separating said mustard from said water; drying said mustard; heating said mustard to a maximum temperature of about 250 C.; distilling said mustard under a maximum pressure of about mm. of mercury; and maintaining throughout said distillation a vapor temperature within the range of approximately C., to approximately C.

3. The method of claim 2, that includes the step of adding to said mixture an anti-emulsion agent before settling said mixture.

References Cited in the file of this patent Industrial and Engineering Chemistry, vol. 11, pages 821 and 822 (1919). 

1. A PROCESS OF PREPARING PURIFIED MUSTARD FROM LEVINSTEIN MUSTARD WHICH COMPRISES WASHING LEVINSTEIN MUSTARD WITH WATER, SEPARATING THE WASHED MUSTARD FROM THE WASH WATER, HEATING SAID MUSTARD TO A TEMPERATURE BELOW THE BOILING TEMPERATURE OF SAID MUSTARD AT THE EXISTING PRESSURE, AND THEREAFTER DISTILLING THE WASHED MUSTARD UNDER REDUCED PRESSURE TO OBTAIN A MUSTARD DISTILLATE OF A HIGH DEGREE OF PURITY. 